#![cfg_attr(docsrs, feature(doc_auto_cfg))]
#![doc = include_str!("../README.md")]
#![cfg_attr(not(feature = "std"), no_std)]

#[allow(unused_imports)]
use std_shims::prelude::*;
#[cfg(any(feature = "alloc", feature = "std"))]
use std_shims::io::{self, Read};

use generic_array::typenum::{Sum, Diff, Quot, U, U1, U2};
use ciphersuite::group::{ff::PrimeField, Group};

#[macro_use]
mod backend;

mod scalar;
pub use scalar::Scalar;

pub use dalek_ff_group::Scalar as FieldElement;

mod point;
pub use point::Point;

/// Ciphersuite for Embedwards25519.
///
/// hash_to_F is implemented with a naive concatenation of the dst and data, allowing transposition
/// between the two. This means `dst: b"abc", data: b"def"`, will produce the same scalar as
/// `dst: "abcdef", data: b""`. Please use carefully, not letting dsts be substrings of each other.
#[derive(Clone, Copy, PartialEq, Eq, Debug, zeroize::Zeroize)]
pub struct Embedwards25519;
impl ciphersuite::Ciphersuite for Embedwards25519 {
  type F = Scalar;
  type G = Point;
  type H = blake2::Blake2b512;

  const ID: &'static [u8] = b"embedwards25519";

  fn generator() -> Self::G {
    Point::generator()
  }

  fn hash_to_F(dst: &[u8], data: &[u8]) -> Self::F {
    use blake2::Digest;
    Scalar::wide_reduce(Self::H::digest([dst, data].concat()).as_slice().try_into().unwrap())
  }

  // We override the provided impl, which compares against the reserialization, because
  // we already require canonicity
  #[cfg(any(feature = "alloc", feature = "std"))]
  #[allow(non_snake_case)]
  fn read_G<R: Read>(reader: &mut R) -> io::Result<Self::G> {
    use ciphersuite::group::GroupEncoding;

    let mut encoding = <Self::G as GroupEncoding>::Repr::default();
    reader.read_exact(encoding.as_mut())?;

    let point = Option::<Self::G>::from(Self::G::from_bytes(&encoding))
      .ok_or_else(|| io::Error::other("invalid point"))?;
    Ok(point)
  }
}

impl generalized_bulletproofs_ec_gadgets::DiscreteLogParameters for Embedwards25519 {
  type ScalarBits = U<{ Scalar::NUM_BITS as usize }>;
  type XCoefficients = Quot<Sum<Self::ScalarBits, U1>, U2>;
  type XCoefficientsMinusOne = Diff<Self::XCoefficients, U1>;
  type YxCoefficients = Diff<Quot<Sum<Sum<Self::ScalarBits, U1>, U1>, U2>, U2>;
}